This invention relates to a light collection device for use with a telescope. In particular, the invention can significantly increase the light collecting capability of a standard telescope, or in certain embodiments may function as a stand alone telescope.
The telescope has had an enormous impact on man""s understanding of the nature and working of the universe. Two general types on telescopes are used by mankind, those used for collecting visible light and those utilized for the collection of x-ray emissions. Regardless of type, x-rays or light rays are gathered and concentrated by the telescope in an effort to analyze what is collected.
The present invention is directed primarily towards optical (light gathering), ultraviolet, and near-infrared telescopes of which there are two primary varieties, the refractor and the reflector. A refractor telescope uses a series of lenses to refract or bend light and concentrate it as it enters through the front aperture of the telescope. On the other hand, the reflector telescope uses a combination of mirrors to collect a large amount of light and focus it so that the light may be seen by the naked eye or recorded by photograph.
The ability of either type (refractor or reflector) of telescope to detect and distinguish distant celestial bodies is dependent upon two important properties of the telescope. The first property is the telescope""s ability to collect and gather light. The light collecting ability is related directly to the size of the light entry aperture, or diameter of the telescope. In general, the larger the aperture, the greater the telescope""s ability to gather light. The more light gathered and brought into focus by the telescope, the more distinguishable the final image will be.
The second important property of a telescope is its ability to magnify the collected light. The measure of a telescope""s ability to enlarge an image is called magnification. The magnification of a telescope is dependent upon the types of lenses used in the telescope, with the eyepiece generally being the most important. The eyepiece allows the gathered light to be viewed by the observer""s eye. Since magnification can be varied on almost any telescope through the use of different eyepieces, a telescope""s ability to view and distinguish distant objects is; normally more dependent upon its light collecting ability rather than its magnification.
The first telescopes developed by man were of the refractor variety. These telescopes gather light through an objective lens (aperture), focus the light to a focal point, and then magnify the light with an eyepiece. Although effective, the objective lens (and hence the light collecting ability) of refractor telescopes are typically limited to a diameter of four inches or less. Refractor telescopes with large lenses tend to exhibit chromatic aberration, which is the appearance of a rainbow halo around the viewed image. Although different types of corrective lenses are available to correct chromatic aberration, the aberration increases as the objective lens gets larger. Additionally, the cost for manufacturing objective type lenses with diameters exceeding four inches increases significantly. Therefore, for the reasons stated above, the cost per unit of aperture for a refractor telescope becomes much greater than for a reflector telescope once the aperture reaches four inches in diameter.
Isaac Newton developed the reflective telescope in roughly 1680. A reflector telescope uses a curved mirror (also known as a primary mirror) to gather and reflect light to a focal point located in front of the mirror. A second flat mirror (known as the auxiliary mirror) then reflects the light through the side of the telescope to a magnifying eyepiece. Another type of reflector telescope is the Cassegrain design. A Cassegrain telescope also utilizes primary and auxiliary mirrors, but the primary mirror has a central hole, and the auxiliary mirror has a convex shape. The convex auxiliary mirror reflects the collected light reflected from the primary mirror back along the axis of the telescope and through the hole in the primary mirror. The most well known example of a Cassegrain telescope is the Hubble Space Telescope.
Although overall they are relatively cost effective, reflector telescopes tend to suffer from a drawback known as xe2x80x9cspherical aberration,xe2x80x9d which is when the light reflected from the primary mirror""s edge is focused to a slightly different point than the light reflected from the center. This causes a visual distortion near the edge of the viewed image causing the image to become elongated near the edge of the visual field. This leads to numerous visual problems, including the problem of stars appearing as if they are comets.
In an effort to correct spherical aberration in reflector telescopes, a hybrid telescope called the compound or the catadioptric telescope was developed. Compound telescopes have a primary mirror located at thie back of the telescope with a glass corrector plate located near the front of the telescope close to the aperture. The corrector plate bends the collected light in an effort to correct spherical aberration so that it all meets at the focal point. One of the most popular types of compound telescopes is known as the Schmidt-Cassegrain telescope. In a Schmidt-Cassegrain telescope, the light rays travel through the aperture and the corrector plate, reflect off of the primary mirror to the auxiliary mirror, and then bounce off the auxiliary mirror through a small hole in the center of the primary mirror, where the light rays are magnified by the eyepiece.
One major drawback with telescopes of the Schmidt-Cassegrain design is the difficulty in producing corrector plates able to correct spherical aberration for large primary mirrors. The larger the primary mirror, the more complex the curvature for the large corrective plate. This increases the difficulty in manufacturing the corrector plate and consequently increases the cost of the telescope. The employment of a corrector plate also increases the overall length of the compound telescope so that it is about twice the length of a traditional reflector telescope with the same focal length.
A second problem with compound telescopes has to do with the difficulty in producing the primary mirror. As the size of the primary mirror increases, the difficulty in achieving the proper curvature and surface polish also increases. Additionally, the thickness of the primary mirror and its mass must increase in order for the mirror to be rigid enough to hold the proper curvature. Very large primary mirrors present difficulties in transportation. In addition, large primary mirrors also can form temperature gradients which may distort the viewing of the reflected image.
The invention disclosed herein is designed to increase the effectiveness of the many different types of telescopes by increasing the amount of light the telescope collects and gathers. In one embodiment of the present invention, a light collection device includes two partial conical surfaces, the first being smaller and located within the second. The partial conical surfaces are generally shaped as a frustum of a cone, being widest at the base and more narrow toward the end where the apex of the cone would be located. The two frustums differ in size, with the inner surface of the larger frustum being highly polished and the outer surface of the smaller frustum being highly polished, both highly polished surfaces being reflective enough to reflect light and electromagnetic rays.
In one embodiment, the invention utilizes right circular cones or frustums. If the inner surface of such a cone or frustum is a reflecting surface, all rays, parallel to the axis thereof, that enter the cone through the base are reflected toward and perpendicular to the central axis of the cone. Similarly, any rays projected perpendicularly toward the axis of a right circular cone will reflect off a polished outer surface and travel in a direction parallel to the central axis. Consequently, two concentric frustum, one within the other, with an inner reflective surface on the outer frustum and an outer reflective surface on the inner frustum that are substantially parallel and orientated such that the reflective surfaces face each other, will xe2x80x9cfunnelxe2x80x9d any rays entering the base of the frustum. Light rays entering the base and traveling parallel to the central axis will be concentrated, exiting the apex of the outer frustum in a direction parallel to the central axis. In other words, light may be collected at the frustums base end and condensed near the opposite end.
Based upon the conical property explained above, if two differently sized frustums can be supported so that the walls of the frustum are held concentric and parallel and mounted to the front of a telescope, the amount of light gathered by the telescope is greatly increased. Hence, through this light funneling technique, the effective area of the aperture is increased. Consequently, the light-gathering device may be used by amateur and professional astronomers alike to increase the power of their telescopes, allowing a cost effective means of viewing distant stars: and galaxies. Larger scale light-gathering devices of this type may also be used to economically increase the light gathered by telescopes in earth observatories or in space based telescopes.
It is believed that frustum pieces may best be machined through either a diamond milling process or a lathing process. The frustum can be spun while the cutting tool remains fixed, allowing the mirror surfaces to be brought near the final reflective tolerance before a final polishing takes place. The same cutting frame set up may be used in the final polishing steps by replacing the cutting tool with pitch tools.
Another aspect of this invention relates to the strength and rigidity offered by the dual frustum assembly. The frustum shape is inherently sturdy and the rigidity may be increased by using braces and supports. Accordingly, a thin layer of polished glass material may be used to increase the reflective properties of the frustum, thereby increasing the effectiveness of the light gathering. The rigidity of the structure helps maintain the integrity of the layer of glass. In another embodiment, both frustums may also be constructed entirely of low expansion glass. The back side of an all glass mirror can be hollowed out by the use of a traditional honeycomb pattern, which reduces the mass.
In yet another embodiment, the dual frustum light-gathering device functions as a traditional stand alone telescope by using a parabolic lens coating or parabolic cylinder reflecting shape on the inner frustum. The parabolic lens coating reflects light in a direction to a focal point where all the light beams converge, rather than parallel to the central axis of the frustum. Using an eyepiece, the operator of the telescope can then magnify the image gathered, allowing the image to be viewed by the user. In another embodiment of the invention, a parabolic covered inner frustum is inverted, and a auxiliary mirror is used to direct the light rays in a manner that allows the light-gathering device to function as a stand-alone telescope-with a shorter overall length. In still another embodiment, the overall length of the light-gathering device is decreased through the use an inverted inner frustum and a parabolic auxiliary mirror.